Variable transconductance amplifier, modulator tube



May 13, 1958 H. J. WOLKSTEIN 2,834,910

A VARIABLE TRANSCONDUCTANCE AMPLIFIER, MODULATOR TUBE Filed Feb. 28, 1955 4 Sheets-Sheet l INVENTOR. #:MERT J Mammy/v 5%4 ywkk Arron/5x May 13, 1958 1-1..1. WOLKSTEIN 2,

VARIABLE TRANSCONDUCTANCE AMPLIFIER, MODULATOR TUBE Filed Feb. 28, 1955 4 Shljets-Sheet 2 44770k/VEK VARIABLE TRANSCONDUCTANCE AMPLIFIER, MODULATOR TUBE Filed Feb. 28, 1955 May 13, 1958 H. J. WOLKSTEIN 4 Sheets-Sheet 3 Ill a Nae/a0; 104100 y 195 H. J. WOLKSTEIN 2,834,910

VARIABLE TRANSCONDUCTANCE AMPLIFIER, MODULATOR TUBE Filed Feb. 28, 1955 4 Sheets-Sheet 4 HH'HH INVENTOR. fiseazzvr- J Woursrz-wv BY I ya Aime/Y5K VARIABLE TRANSCONDUCTAN CE AMPLIFIER, MODULATOR TUBE Herbert J. Wolkstein, Newark, N. 1., assignor to National Union Electric Corporation, Orange, N. 1., a corporation of Delaware Application February 28, 1955, Serial No. 490,984

8 Claims. (Cl. 315-12) This invention relates to electron discharge tubes and more especially it relates to such tubes for use as amplifiers or modulators.

A principal object of the invention is to provide an improved variable transconductance tube whereby an extremely wide variation of transconductance can be achieved without materially shifting the operating point on the input-output current characteristic curve.

Another object is to provide a novel form of amplification tube employing a primary and a secondary ernissive output target or electrode, whereby the signal output of the tube is achieved around zero net direct current .flow. A feature of the invention resides in an improved amplifier or modulator system embodying a novel tube construction whereby the system can be switched from its operating quiescent state to cut-off without any substantial rise or fall in the voltage at the plate or output electrode; thus eliminating the transients which usually accompany such change-over with conventional tubes.

Another feature relates to an improved amplifier or modulator system employing a novel tube construction, whereby amplification of modulation can be achieved without any substantial direct current load dissipation.

A further feature relates to a novel electron tube whereby push-pull class A amplification can be achieved with only a single-ended output, while at the same time this output is obtained at zero net direct current flow.

A still further feature relates to the novel organization, location, and interconnection of parts which cooperate to provide an improved variable transconductance tube.

Other features and advantages not particularly enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

In the drawing, which shows by way example certain preferred embodiments,

Fig. 1A is a schematic plan view of a tube embodying the invention;

Fig. 1B is a schematic plan view of a modification of the tube of Fig. 1A;

Fig. 2 is a composite schematic diagram and graph explaining the operation of the tubes of Figs. 1A and 1B;

Fig. 3A is a graph showing certain operating characteristics of the tubes of Figs. 1A and 1B;

Fig. 3B is a graph showing the characteristics of a conventional grid-controlled amplifier tube;

Fig. 4 is a series of interrelated graphs explaining how the transconductance control of the tubes of Figs. 1A and 1B is achieved;

Fig. 5 is a schematic wiring diagram of a modulation system employing the tube of either Fig. 1A or Fig. 113;

Fig. 6 is a wave diagram showing the amplitude of the radio frequency carrier applied to the input of Fig. 5;

Figs. 7A, 7B, 7C, and 7D are respective wave diagrams showing various forms of modulation wave inputs applied to Fig. 5;

Figs. 8A, 8B, 8C, and 8D are respective wave diagrams of the output currents in the system of Fig. 5 correspond- 25,834,911 Patented May 13, 1958 2 ing to the respective modulation input waves of Figs. 7A-7D;

Figs. 9A, 9B, 9C, and 9D are wave diagrams of the output current of a conventional modulator not employing a tube according to the invention.

Referring to Fig. 1A, the numeral 10 represents a suitable evacuated enclosing bulb or envelope which encloses a series of electrodes according to the invention. These electrodes comprise any well known heatable electron emitting cathode 11 associated with which is a control grid or electrode 12. Preferably this electrode is of a shape such that it electrostatically forms the electrons from the cathode 11 into a linear well-defined beam 13. Located within the path of the beam 13 is an electron acceleration electrode 14 having an opening 15 through which the beam passes. The beam then passes between a pair of electrostatic deflection plates 16, 17, which are located on opposite sides of the beam trajectory and are energized by a voltage to deflect the beam 13 perpendicular to its trajectory, namely in a direction parallel to the plane of the sheet of drawing.

The beam 13 then passes through a foraminous electron collector electrode 18 which may be in the form of a woven or mesh wire grid. The collector electrode 18 can be connected to the acceleration electrode 14 so that it collects the secondary electrons and returns them to ground, thus preventing their reaching the deflection plates 16 and 17.

Located on the opposite side of the grid 18 from the plates 16 and 17 is an output anode or target electrode 19. This electrode may be in the form of a metal plate bent back upon itself so that it is provided with a front bentback portion 20 and a rear portion 21, both of which are substantially parallel to each other or normal to the beam trajectory. The portion 20 of the electrode 19 is shorter in length than the portion 21. The length of portion 20 for example may be one-half the length of portion 21. The electrode 19 is mounted symmetrically with respect to the plates 16 and 17 so that when the beam 13 is in its normal or undeflected position, half of the beam is intercepted by the portion 21 and the remaining half of the beam is intercepted by the portion 21 of the output electrode 19.

In accordance with the invention, the front surface of portion 20, that is the portion facing the cathode 11, is coated or treated in any well known manner so as to make it an efiicient emitter of secondary electrons. As is Well known in the electron tube art, such a surface, when impinged upon by the high velocity primary electrons in the beam 13, emits secondary electrons in a ratio greater than one, so that the potential of the portion 20 swings in a positive direction in proportion to the quantity of primary electrons impinging thereon from the beam 13. On the other hand, the forward surface of portion 21 facing the cathode 11 is uncoated so that it does not act as a secondary electron emitter. However, in order to take care of any incidentai or unfdesirable reversely moving electrons that may be emitted or reflected from the portion 21, there is located in spaced relation to the front face of portion 21 any well known conductive forarninous grid or mesh electrode 22 which acts as a secondary electron suppressor only for the anode surface of the element 21. By suitable energization and biasing of the various electrodes with respect to the cathode 11, it will be clear that the instantaneous potential of the target electrode 19 will be a function of the position of the beam 13. In other words, the portion 20 of the output anode 19 acts as a dynode tending to change the potential of the said target electrode in a positive direction as the intercept between the portion 20 and the beam 13 increases and conversely the potential of the. target 19 swings in a negative direction as. the intercept between the portion 21 and the beam 13 increases. The portions 20 and 21 are, of course, directly connected together by being formedfronr the same bent back metal sheet. However, if desired, the portions 20 and 21 may be in the form of separate metal sheets which are. directly connected together by' a, suitable conductive strap so that the electrode 19 constitutes a single output electrode connected to a common output load circuit.

Thus, deflection of the beam 13 by the plates 16 and 17 provides for addition of the currents at the portions 20 and 21 through the common load.

Fig.2 shows the relation between the position of the beam '13 with respect to. the target 19 and the current inthe output circuit. In Fig. 2 the curve 23 shows. the relation between the current from the portion21 (which for convenience will be referred to as the anode) and the position of the beam 13. The dot-dash line 24 represents the position of the center line of the beam in its normal or undefiected condition, wherein the beam is equally intercepted by the dynode 20 and the anode 21. Therefore, as the beam 13 is deflected towards the right the positive component of the output current rises. The curve 25 represents the relation between the beam position and the dynode current from which it, will be seen that as the beam 13 is deflected to the right the negative current from the dynode decreases while the positive current from the anode increases. The net result of the combined currents'from the anode and dynode are thus 4 is. symmetrical with respect .to the zero direct. current. line 27.

Fig. 3B shows the grid-transfer characteristics of a conventional modulator tube from which it will be seen that the tube must operate on the curved portion of the characteristic resulting in a non-symmetrical output current with respect to. the zero line 27. In other words, the modulation can be achieved in the tubes, according to the present invention, while operating on a linear portion of a characteristic curve, whereas in a conventional tube modulation is. achieved by operation on a curved portion of the characteristic curve.

Fig. 5 shows schematically a typical system for using the tubes of Figs. 1A and 1B as a modulator. The elements of Fig. 5, which are the same as those of Figs. 1A and 1B, are designated by the same numerals. The radio frequency or carrier input voltage from any well known source may be applied through a coupling condenser 31 across the deflector plates 16 and 17'. In the well known manner, plate 17, for example, may be grounded and the potential of plate 16 may be varied above and below ground by means of the radio frequency input voltage. The cathode 11 is biased with respect to ground by anywell known self-biasing circuit, and likewise the control grid 12 is negatively .biased with respect to ground by any well known biasing; circuit. The accelerating electrode represented by the dotted curve 26 which is. symmetrical about the zero net direct current line 27. It will be observed that the leveling off of the primary and secondary currents at both extremes of the beam deflection indicates saturation. For convenience of description, the composite curve 26 is referred to herein as the anodyne characteristic curve. For purposes of illustration, the

' primary maximum current at the anode 21 resulting from the primary electrons in the beam striking the anode. 21 is equal to the secondarymaximum component achieved by the impingement of the beam 13 on the dynode 20. This, of course, occurs only if the secondary emission ratio of the surface 20 is equal to two at the operating voltage of the surface 20. This mode of operation allows twice the deflection transconductance obtainable over conventional beam deflection amplifiers which do not to act as a dynode, while the rear surface of the target 19 is uncoated so that it does not act as a secondary emitter. The beam 13 is arranged to strike the dynode surface of target 19 directly whereas the anode surface 21a of the target 19 cooperates with a curved electr0- static deflector plate 28 to cause the primary electrons in the beam 1310 be deflected towards the anode surface 21a without, of course, striking the deflector plate 28. Otherwise the operation of the tube of Fig. 1B is identical with that of Fig. 1A.

Fig. 3A shows the relation between the output current and an input signal voltage across-the plates 16- and 17. In this figure the graph 29 represents the input deflection voltage applied across the said deflector plates 16 and 17' and the curve 30 represents: the output current at thev common load circuit. It will be observed that with this arrangement it is possible to operate'on the linear portion of the compositeoutput curve 26 and the output-current 14. and the collector electrode 18 likewise are biased positively with; respect to the cathode. The suppressor grid 22 can be directly connected to the cathode 11. The composite dynode-anode target 19 is connected to a suitable positive potential through a load resistor 32, and the common output circuit is connected directly to theelectrode 19 by the. conductor 33. The modulation signal from any suitable input source is applied through a con.- pling condenser 34.. to the grid 12.

For dynamic operation of the tube, the various biasing potentials. are adjusted so that the beam deflection is centered with respect. tolthe. surface 20 and 21, and the net current through the output circuit is zero corresponding tov point Q of Fig. 2. This mode of operation therefore allows signal modulation with no direct, current load dis sipation,

Fig. 4' illustrates the relation between an input signal applied to grid. 12. and output signal from electrode 19 for diflerent negative lblaSeS applied to grid 12. The interpretation .of Fig. 4' is that it is possible to obtaininfiinite variation of transconductance without production of undesirable transients in the output circuit. Qperation of the system around the zero not direct current flow permits modulation of the beam current by the control grid 12 without producing an output transient or change in directcurrent voltage output level through the load. At balance, namely when primary current component from element 21 is equal to secondary electron current from element 20, any reduction in the total beam current does not affect the conditions of net zero load current. This clearly is illustrated by the series of curves of Fig. 4. Maximum output, is obtained atv zero grid bias for a given deflection modulating voltage. For smaller values. of beam current, that. is with an increased negative bias on thegrid 12, less output is obtained. The control of beam current magnitude, as indicated, thus regulates the trans-' conductance. of the device without shifting the operating point. In conventional amplifier tubes, changing the bias of. the amplifier control grid necessarily shifts the operating point. This condition in a conventional amplifier is evenmorev pronounced when the amplifier is driven from its operating, point to cut-off. Under that condition, a sharp rise inplate voltage takes place.

The relative operations of the system of Fig.v 5}, as compared with a conventional modulator tube for difierent shapes of input modulation waves, is illustrated in Figs. 7A.7D,. 8A-8D,. and 9A-9D. Assume that the radiofrequency or carrier input is of constant peak. ant-- plitude and wave shape as illustrated in Fig. 6, and let it be assumed that the wave shape of the modulation signal is that illustrated in Fig. 7A. Fig. 8A shows the corresponding output of the system of Fig. 5, whereas Fig. 9A shows the corresponding output for a conventional modulator tube. A comparison of these respective output characteristics indicates that the contour of the radio frequency output of the system of Fig. follows the wave shape applied to the control grid. Thus, if a square modulation wave input is used, as shown inFig. 7B, a square wave of radio frequency output free from transients is produced as illustrated in Fig. 8B. On the other hand, with the conventional amplifier, non-square wave output is obtained with substantial transients. Similarly, if the modulation input wave is a sine wave, as illustrated in Fig. 7C, the output of Fig. 5 produces similar' sine wave characteristics which vary symmetrically with respect to the zero line. An entirely different characteristic is obtained with the conventional modulator, as is illustrated by the curve of Fig. 9C. Furthermore, the application of a negative linear pulse to the control grid 12 of Fig. 5 as illustrated by the signal curve of Fig. 7D, produces a linear variation of transconductance from a maximum value ot a zero value without affecting output linearity or producting transients, as is shown by Fig. 8D. On the contrary, when such an input negative pulse is applied to the conventional modulator, it produces a non-symmetrical output and transients, as illustrated by Fig. 9D.

The tubes and system of this invention have been used in practical laboratory circuits to eliminate undesirable noise and transient conditions encountered in various radio receiver equipments. It was found that conventional tubes used for similar noise suppression circuits produced undesirable transient and noise conditions when blanking wave shapes are applied to eliminate the original noise. Furthermore, as indicated in the above description, the tubes according to the invention have excellent characteristics for low level balance modulation purposes.

Various changes and modifications may be made in the disclosed embodiments without departing from the spirit and scope of the invention. It will be understood, of course, that the invention is not limited to the use of the tube wherein the ratio of secondary emission to primary emission is 2 which, of course, represents the ideal case for optimum symmetry. This ratio may be any other desired value consistent with the percentage of symmetry desired in the output of the tube. Thus, operation about zero load current is achieved, in practice, by deflection centering the line beam on the target current. This provides for no-load dissipation and linear operation at a position slightly off the center line of the target.

What is claimed is:

1. Electron tube apparatus comprising, means to develop a deflectable electron beam, electrode means to control the beam current, target electrode means having front and rear portions with respect to the beam trajectory one portion being a dynode and the other an anode, said target means being mounted transversely of the beam trajectory so that when the beam is in its normal undefiected position it impinges in a predetermined ratio on both the dynode and the anode to produce a zero combined current from the dynode and the anode, means to deflect the beam to vary said ratio of interception and thereby to vary the said combined current, means connecting the dynode and anode in common to the same output load, and the entire dynode surface impinged upon by the beam having substantially uniform secondary emission characteristics.

2. Electron tube apparatus according to claim 1 in which a secondary electron suppressor is provided for said anode only.

3. Electron tube apparatus according to claim 1 in which said beam in its normal undefiected position equally intercepts the anode and dynode, and the dynode has a secondary-to-primary emission ratio of approximately two.

4. Electron tube apparatus comprising, a cathode to develop a deflectable electron beam having a substantially linear trajectory, a beam control electrode negatively biased with relation to said cathode to determine the beam intensity, output target electrode means comprising a dynode and an anode in lateral spaced relation with respect to the beam trajectory and conductively connected to form a single output electrode, said beam in its normal undefiected position impinging in a predetermined ratio on both the dynode and the anode, means connecting both the dynode and the anode together and in common to the same load so that both the dynode and the anode are at the same direct current potential when not impinged upon by said beam, a secondary electron suppressor electrode for said anode only, and signalcontrolled means to deflect the beam to produce in said load a single composite currentwhich is the resultant of the combined variable intercept of said beam by the dynode and the anode respectively.

5. Electron tube apparatus comprising, a cathode to develop a deflectable electron beam having a substantially linear trajectory, a beam control electrode negatively biased with relation to said cathode to determine the beam intensity, output target electrode means comprising a first surface extending transversely to the beam trajectory and variably intercepting the beam in accordance with the extent of beam deflection, said first surface being a dynode, said target means having a second surface also variably intercepting the beam in accordance with the extent of deflection of the beam, said surfaces being located in lateral spaced relation to each other in the path of the beam so that when the beam is in its normal position it is intercepted in a predetermined ratio by both surfaces, means connecting both surfaces directly electrically and to a common load circuit so that both surfaces are at the same direct current potential when not impinged upon by the beam, means to deflect the beam to produce in said load circuit a single composite direct current which is a resultant of the combined intercepts of the beam by said surfaces, a suppressor electrode located between said surfaces, and an electron collector electrode located in front of both said surfaces on the side facing the cathode.

6. Electron tube apparatus comprising, a cathode to develop a deflectable electron beam having a substantially linear trajectory, a beam control electrode negatively biased with relation to said cathode to determine the beam intensity, output target electrode means comprising a first surface extending transversely to the beam trajectory and variably intercepting the beam in accordance with the extent of beam deflection, said first surface being a dynode, said target means having a second surface also variably intercepting the beam in accordance with the extent of deflection of the beam, a secondary electron suppressor for said second surface only, said surfaces being located in lateral spaced relation to each other in the path of the beam so that when the beam is in its normal position it is intercepted in a predetermined ratio by both surfaces, means connecting both surfaces directly electrically and to a common load circuit so that both surfaces are at the same direct current potential when not impinged upon by the beam, means to deflect the beam to produce in said load circuit a single composite direct curent which is a resultant of the combined intercepts of the beam by said surfaces, and both said surfaces are in the form of plates which are located forwardly and rearwardly of each other along the beam trajectory, said plates extending parallel to each other but being directly electrically joined so as to be at the same direct current potential when not impinged upon by said beam.

7. Electron tube apparatus comprising, a cathode to develop a deflectable electron beam having said substantially linear trajectory, a beam control electrode negav 7 t tiveIy biased with relation to said cathode to determine the beam intensity, output target, electrode means comprising a first surface extending transversely to the beam trajectory and variably intercepting the bearn in accordance with the extent of beam deflection, said first surface being a dynode, said target means having a second surface also variably interceptingthe beam in accordance with the extent of deflection of the beam, a secondary electron suppressor for said second surface only, said surfaces being located in lateral spaced relation to each other in the path of the beam so that when the beam is in its normal position. it is intercepted in a predetermined ratio by both surfaces, means connecting both surfaces directly electrically and to a common load circuit so that both surfaces are at the same direct current potential when not impinged upon by said beam, means to deflect the beam to produce in said. load circuit a single composite direct current which is' a resultant of the combined intercepts of the beam by said surfaces, and both of said surfaces are formed horn a single metalpl'ate bentback; upon itself withjone bent-back leg shorter than the other tfromHwhichr tii i pa ed-, Y t

8.,Electrqnfl tube apparatus according to clair n f 7 'in' which 1 a secondaryj electron suppressor grid is located" between the said bent-back portions of said plate and an electron collectonelectrode is located in. front of both said, bent-back portions on the side facing the cathode.

References'Cited' in the file of thisv patent 'UNI'EED STATES PATENTS 7 

